The stereophonic recording and playback of sounds has been known for some time.
Sound is picked up by at least two microphones fixed in a precise position and orientation and considered to be xe2x80x9cstrategicxe2x80x9d with respect to the sound source.
The sounds coming from one of these two microphones, or from a set of microphones, are recorded on one track while the sounds coming from the second microphone, or from the second set of microphones, are recorded on another track, distinct from the first one.
Recorded sounds are played back by at least two speaker boxes (or loudspeakers) suitably positioned and oriented.
The binary nature of any stereophonic system comes from the transposition to sound of stereoscopy, dating back earlier, and itself based on the binocular vision of man.
While the optical systems that make use of this binocular vision, holograms, bipolar images or anaglyphs, for example, reproduce visual relief fairly well (at the expense of using many artifices, however), the same is not true of stereophonic systems, because of their very simplicity based on the fact that, naturally, man hears all the sounds in space from two sources alone.
In other words, all complex sounds distributed through a three-dimensional space, including different levels, are reduced to a single plane, joining together the speaker boxes and at their level alone.
This simplification is generally accepted because the human brain reconstitutes a true space virtually, particularly through the balance that is deliberately constructed between different sound sources, so that the listener has, or rather believes he has, an impression of relief.
It is not necessary to go into detail on the statement that relief implies three dimensions and not two, and it is easy to understand that, however far one goes in improving ad-hoc sound reproduction, stereophony has its own limitations simply because it limits the number of sound sources offered to the listener""s hearing to two, themselves subject to the limitation on recording tracks, with no possibility of a third dimension.
To give context to the State of the Art, the following documents may be cited:
Article by Mr A Laracine published in the journal xe2x80x9cZERO VUxe2x80x9d, pages 40, 42, 44, 46, 47 and 48, which states that . . . xe2x80x9cstereophony is only one stagexe2x80x9d and that xe2x80x9cthe listener does not always find in it the opportunity for intelligent listening, but nevertheless the main ones and a large part of his liberty, and therefore his listening comfortxe2x80x9d,
The author also points out that, in the case of orchestral music, . . . xe2x80x9cif the general balance of the work has been obtained by the sound recordist, thanks to good positioning of the microphone, any other major action taken (level, corrections, difference in presence) will be experienced as a sort of xe2x80x9cpleonasmxe2x80x9d of sound and will distract the listener""s attentionxe2x80x9d. And, further on: xe2x80x9cOne solution consists in using cardioid microphones positioned 17 cm apart, their axes forming an angle of 110xc2x0 between them. All calculations, all measurements and the very numerous experiments all combine to prove that this system is the best possible compromise. It is known by the system name AB O.R.T.F. since it was developed in the acoustic laboratory of the former O.R.T.F.xe2x80x9d
Naturally, all known recording systems concern positioned microphones, fixed once and for all throughout the recording. This is demonstrated by this extract from the same article:xe2x80x9d . . . in the case of the picking up of sounds that are close together, a xe2x80x9ctearing apartxe2x80x9d of space is observed. This tearing apart is the same as that experienced by a spectator (sic) if he approaches the sound sources in the same wayxe2x80x9d. Since the number of sound sources is always equal to two and since they occupy a fixed position from which they cannot be removed, the angle at which the listener perceives the sounds coming from these two sources varies depending on the space he occupies in relation to them and . . . xe2x80x9cthe difficulty arises from the fact that it is not possible to ask a listener to move closer to his speaker boxes temporarily. It is therefore necessary to find ways of creating faults with the O.R.T.F. pair to compensate for its unsuitability for certain situations. It is possible . . . to cause the pair to pivot on its axis in order to cause it to occupy an intermediate position between the horizontal plane and the vertical planexe2x80x9d.
The existence of an occupied position clearly demonstrates, here too, that the pair is positioned and fixed.
In the Internet publication, at the address http:  www.stereolith.ch, entitled xe2x80x9cStereolith(copyright) systmexe2x80x9d, the following is stated: xe2x80x9cDuring a stereophonic recording, the sound space is encoded by a two-channel (dipole) matrix. For this, a pair of microphones is used, for example. Each of the microphones provides a signal that is slightly different depending on the location of the sound source. This slight difference is of great importance. The spaciousness of the recording is depends solely on this difference.xe2x80x9d And further on: xe2x80x9cIn modem electronic music the vital sound space is produced in the studio, by means of special three-dimensional (sic) processors.xe2x80x9d
This same publication contains the following information regarding listening by means of speaker boxes: xe2x80x9cOutside the ideal listening point, it is impossible for our brain to reconstitute the sound image: the elementary information is missing or distorted. This means that, very often, we obtain merely bi-channel reproduction rather than stereophonic reproductionxe2x80x9d.
The document published by Schoeps GmbH, Spitalstr. 20, 7500 Karlsruhe 41 (Germany) describes a pair of microphones associated with a sphere based on the human head, which constitutes an assembly that has to be fixed to a xe2x80x9cstrategicxe2x80x9d location: xe2x80x9cThe new approach should take account of all the parameters characterising the sound source and its locationxe2x80x9d. This therefore definitely relates to an immobile sound source, situated in a given location relative to the pair of microphones, which is itself immobile. The technical specification of this apparatus requires, furthermore, that the sound pick-up angle is fixed at around 90xc2x0 and that there is:
an accessory supplied with the device itself, which is an xe2x80x9caccessory for suspending the microphone with a ball joint. Total weight: around 0.5 kgxe2x80x9d.
xe2x80x9ca ball joint for mounting on a standxe2x80x9d.
Spheres carrying two microphones do exist in different variants, one of which is described in the patent document EP 0 050 100, all providing improvements to the structure of the sphere, in order to bring it as close as possible to a genuine human head, in the hope of making the recording conditions coincide with the listening conditions but, as has been indicated above, the limitation of stereophony is in its binary nature and, therefore, in the static situation of the microphones and speaker boxes, located respectively upstream and downstream of the recording tracks.
Patent document FR 2 290 811, which describes a piece of apparatus for picking up sounds intended to eliminate sounds considered to be interference in comparison with those that are intended to be picked up, this device comprising just one or two microphones, depending on whether the apparatus is intended for a single person or for two. One example of using this apparatus is for the direct transmission, without recording, of words spoken by one or two people located in a moving vehicle, by means of powerful loudspeakers. Another example of the use of this apparatus is to integrate it into a loudspeaker-type telephone.
The result sought is the purity of the transmitted sounds, obtained by eliminating echo, ambient noise and open-air sounds.
Patent document DE 1 239 355, which describes a piece of apparatus comprising a stand and two microphones that can be oriented with respect to a support fixed to the stand. This apparatus is therefore fixed and its microphones are capable of movement with respect to the place where the apparatus is placed.
Patent document EP 0 186 996, which describes a microphone with a particular structure allowing it to be very directional when it is placed in a precise position with respect to the sound source. The microphone is therefore fixed and, like the device in the document FR 2 290 811, tends to avoid ambient noise and echo arising from the acoustic characteristics of the location where the sound is picked up.
It should be noted that this document does not cover recording or transmission of sound, since it is limited to the structure of a microphone and the description of FIG. 4 seems to signify that the invention is applied to what is known as a xe2x80x9chands-freexe2x80x9d car-phone.
The present invention relates to a method that is different from the known ones, based on very realistic sound transmission, i.e. close to reality, which presupposes in particular high xe2x80x9creliefxe2x80x9d and the presence of ambient sounds, corresponding to real conditions. In this way the invention makes it possible to reconstitute, on listening, a three-dimensional sound space, including the vertical levels and the spaces in front of and behind the listener.
To this end, the subject-matter of the invention is a method intended for the picking up of sounds coming from at least one sound source, for the recording of said sounds and their play-back, by means of a sound pick-up assembly, a recording medium and a transmission assembly.
the sound pick-up assembly being composed of at least two microphones, the relative position of which is constant,
the recording medium being of any known stereophonic type, particularly with at least two tracks,
the transmission assembly comprising at least two members such as earphones, loudspeakers or speaker boxes,
characterised in that sounds are picked up simultaneously by the two to microphones, known as xe2x80x9crightxe2x80x9d and xe2x80x9cleftxe2x80x9d respectively and that these two microphones are displaced together with respect to said sound source, particularly by causing the distance and/or height of each microphone to vary differentially with respect to that source, i.e. that one of them is brought doser to the sound source when the other is moved away and vice versa, equally well by either of the two faces of the virtual plane that extends from one to the other, it being possible therefore for the right microphone to become the left microphone and vice versa, it being possible also for the two microphones to be moved simultaneously closer to and further away from said sound source.
The invention also has as its subject-matter a device comprising a sound pick-up assembly, a recording medium and a transmission assembly,
the sound pick-up assembly being composed of at least two microphones, opposite each other and held rigidly at a distance from each other that is close to that of the ears of an ordinary human being, and by a sound insulation screen inserted between them,
the recording medium being of any known stereophonic type, particularly with at least two tracks,
the transmission assembly comprising at least two members such as earphones, loudspeakers or speaker boxes,
characterised in that the sound pick-up assembly has no fixing or immobilisation unit, so that it can be displaced and/or oriented at any time, either manually or by kinematic means making it possible to present the microphones to the sound source, equally well by either of the faces of the virtual plane that extends from one to the other and in any intermediate orientation between these two extreme situations.